1. Field of the Invention
The present invention relates to a technique for locating position of a pointer or the like, and more particularly, the invention is to provide such a position locating technique that is superior to the operability of a pointer, such as a computer mouse, and is suitable for a pointing device realizing barrier free, for example, upon operating mobile devices represented by notebook computers.
2. Description of the Related Art
As a pointing device for a personal computer, various kinds of devices have been used, such as computer mice, track balls, joysticks and sheet-like devices. According to the reports relating to the operability of the devices, mice have the best operability in speed and accuracy upon positioning, and therefore, a mouse is to be appended even in the case of mobile environments when the operability is prioritized.
However, in view of increasing variety of the mobile environments and increasing demands in input of characters and images, there is importance in developing pointing devices having good operability other than mice. Furthermore, because there are a number of cases where difficulties occur on operating mice and pens, it is demanded to develop such a new input device that solves the problem from the standpoint of barrier free.
Several kinds of devices have been developed to meet the demands. For example, there are such techniques that a position on a plane is located by using a special tablet, such as the position input tablet produced by Wacom Co., Ltd., and a position on a plane is located by using a two-dimensional semiconductor sensor (PSD) and a lens as disclosed in JP-A-5-25525.
Furthermore, JP-A-10-9812 discloses a technique for locating a position of a light source with a small and inexpensive device, in which light emitted from an input device is measured with a device constituted with photoelectric conversion elements (photodiode (PD)) combined in an L-shape arrangement.
The position input tablet is disadvantageous in miniaturization because it requires such a tablet below a display screen that has a larger area than that of the display screen, and it is impossible to replace only the display screen. Furthermore, there are some cases where the device is difficult to be used by persons having dysfunction of upper extremities because a pen is necessarily moved on the surface of the tablet. Moreover, the device uses an electromagnetic induction system, and thus it has a problem in that there is limitation in reducing the cost.
The system disclosed in JP-A-5-25525 has such an advantage that it enables a pointing operation in an arbitrary region in space, but it has been decided that the device is insufficient as a pointing device of a mobile equipment, which is suffering severe price-reduction, due to the use of expensive PSD and hence, has not yet been put into practical use.
In the system disclosed in JP-A-10-9812, cost reduction is realized since a photoelectric conversion unit formed by combining two photoelectric conversion elements is used as a fundamental unit, but it has a problem in accuracy because the distances between an indicating device (light source) and the respective photoelectric conversion elements are fluctuated by movement of the light source. For example, the device generates an error of about 8 mm upon measurement on an A-4 size plane, and the error is further increased by tilting the light source.
As described herein, the conventional techniques require a large tablet or an expensive measuring device other than a display screen, and those techniques that solve the problems suffer considerable errors.